The present invention relates generally to semiconductor integrated circuits and more specifically to integration of waveshaping functions into an integrated circuit that drives a differential signal onto a local area network.
U.S. Pat. No. 5,357,145 titled Integrated Waveshaping Circuit Using Weighted Current Summing and Issued Oct. 18, 1994 describes relevant background for understanding the present invention, as well as describing one conventional solution to on-chip wave synthesis.
Various network protocols such as IEEE Standards 802.3 (Ethernet) and 10Base-T (twisted pair), both hereby expressly incorporated by reference for all purposes, define operational characteristics for various data signals. To implement a data transmitter for twisted pair wiring using an integrated circuit solution, many conventional systems rely on external filter elements to properly shape the output wave.
U.S. Pat. No. 5,357,145, hereby expressly incorporated by reference for all purposes, illustrates a solution to wave shaping incorporating a weighted sum solution that provides an output waveform designed to represent a shape of an output signal after it has passed through a filter. The solution disclosed in the U.S. Pat. No. 5,357,145 provides a plurality of current cells that are controlled in a fashion so that output contributions of the various cells provide the desired wave shape. Generically, this conversion process defines a digital to analog (D/A) converter or DAC implementation.
For effective operation, construction and control of the current cells is important to provide a robust, fast, and reliable D/A converter for use in waveform synthesis. The solution described in U.S. Pat. No. 5,357,145 provides a current cell that may have excessive parasitic capacitance that can limit an operational speed of the D/A converter.